This invention pertains to fabrics designed and intended primarily for use in winter weight underwear. However, since the fabrics of the invention have an insulating quality, their use is not limited to winter underwear garments. They have utility wherever fabric warmth is desired, for example, in the manufacture of sweaters, sportswear, blankets and the like.
From time immemorial it was conventional for winter underwear fabrics to be sold by weight, for the reason that, in general, the heavier the fabric the warmer the garments made from it. The reason for this is that textile fibers entrap air to a substantial degree, and it is the entrapped air which gives a fabric its insulating quality. Thus, the insulating or thermal effectiveness of a fabric used in making cold weather garments, such as winter underwear, is determined by the amount of air entrapped in the fabric. Accordingly, in the days of yore, winter wear fabrics were designed on the theory that the heavier the fabric by weight, the warmer it would be.
In more recent years, however, fabric designers have developed new fabrics constructed with air-entrapping cells or pockets on one or both sides which provide dead air spaces in the fabric. Such fabric structures trap more air than that entrapped by the fibers alone, and thus enhance the insulating quality of the fabric. Knitted fabrics constructed with a multitude of such air pockets or air-entrapping cells are known as "thermal" fabrics.
The air-entrapping cells in such fabrics are three dimensional cavities having spaced top, bottom and side walls and a floor, which trap and retain air warmed by the heat of the human body. The trapped air gives the fabric an enhanced heat insulating or heat retention quality, thus adding to its insulation, warmth or "thermal" quality.
The original thermal fabric, first known as "waffle knit" fabric, was developed by the U.S. Navy for military use in about 1951. The Navy's waffle knit fabric is a flat, warp knit fabric made on a double needle bar raschel knitting machine. It soon found acceptance for civilian use in underwear, and became known popularly as "thermal underwear". A brief history of the Navy's waffle knit raschel thermal fabric will be found in Professor William E. Schinn's article "The Philip Model PT/RR Machine" published in the Apr. 1968 issue of "The Knitter" magazine, beginning at page 37.
A great interest soon arose in the underwear industry for developing a competing weft knit thermal fabric which could be made on conventional circular knitting machines. A weft knit thermal fabric eventually was developed, for which Morgan U.S. Pat. No. 2,839,909 was granted. The Morgan patented fabric is made on a multifeed circular rib knitting machine having dial and cylinder needles disposed in a 2.times.2 rib knitting arrangement. Its air-entrapping cells are produced by alternate triple tucking, first on one set of needles, then on the other set of needles, the non-tucking needles knitting plain stitches. The Morgan thermal fabric is characterized by spaced groups of tuck strands extending across the valleys formed between the ribs of the fabric, the ribs forming the side walls of the air-entrapping cells and the spaced tuck strands forming the top and bottom walls of the cells.
Later on, a second weft knit thermal fabric was developed utilizing the Philip Model PT/RR knitting machine, for which Philip U.S. Pat. No. 3,568,475 was granted. The PT/RR machine is a multifeed 1.times.1 circular rib knitting machine using the flexer principle to rack the dial needles. In knitting the Philip patented fabric, the machine is arranged for knitting a full cardigan fabric. Selective racking of the dial needles is utilized, whereby the needles assume a 2.times.2 rib relationship during knitting of the fabric. Because the air-entrapping cells in succeeding rows in the Philip thermal fabric are staggered, the fabric more nearly simulates the raschel thermal fabric in appearance than does the earlier Morgan thermal fabric.
Subsequently, a third weft knit thermal fabric was introduced by J.E. Morgan Knitting Mills, Inc. of Tamaqua, Pa. which simulates yet more closely in appearance the raschel knit thermal fabric. This fabric is known in the trade as "circular raschel"because of its close simulation to the raschel thermal fabric. It is composed of repetitive sequences of knit, tuck and welt stitches which produce multiple air-entrapping cells disposed in staggered relationship on both sides of the fabric. The circular raschel thermal fabric also is knitted on a 1.times.1 circular rib knitting machine. Needle selection means are operative to select needles in alternating and repetitive sequences for knitting, tucking and welting in recurring cyles to produce a weft knit thermal fabric incorporating air-entrapping cells constructed of knitted stitches, tuck loops and floats.
For many years winter wear garments made from the raschel, Morgan, Philip and circular raschel thermal fabrics have been sold in the United States. The manufacture and sale of such thermal garments still is taking place.
In the knitting of fabrics generally, it is old practice to knit two or more yarns into a fabric in such a manner that one of the yarns appears on one face of the fabric and a different yarn appears on the opposite face of the fabric. In weft knitting, "plating"is a common practice in hosiery manufacture, wherein fabric is knitted of two yarns which may differ in color or other characteristic. The plated fabric is knit so that one yarn is visible on one side thereof and the other yarn is visible on the opposite side. Morancy U.S. Pat. No. 2,946,210 discloses a rib knit fabric formed of inelastic, elastic and stretch yarns and knitted so that the stretch yarn appears on the inner side of the fabric to provide a relatively soft texture, while the inelastic yarn is disposed on the outer face of the fabric to provide a relatively stiff and smooth texture.
Napping is a decades-old practice in which a small portion of the yarns on one or both sides of a knitted or woven fabric are raised mechanically to provide a fibrous surface. Usually, napping is carried out by causing the fabric to pass over a rotatable cylinder having teeth or spikes on its periphery which pick up the surface fibers of the yarns to a slight extent without tearing or otherwise damaging the fabric. Morgan U.S. Pat. No. 2,839,909 aforesaid discloses the napping of a knitted thermal fabric.